Aesma's Spine is the tallest structure in Throne (excluding the Red City), if it can be called a structure. It is where the warrior-hermit devotaries of Aesma gather in large numbers on their endless pilgrimage. The followers of Aesma are usually warrior-hermits who disdain society and live a ragged and violent existence. They are good drinking partners.
Her devotees, which includes the Belligerent Knights, gather in a giant mosh pit where they party and punch each other to commune with their god. Some sections of petrified bone are chipped away so pilgrims can "do a line of the spine".
The creation of her universe (which was a giant fuck you to YISUN/everything) was so violent that it scattered her body parts all over the Wheel. A subset of her devotaries journey to find them so that they may reassemble and resurrect The Metal God.